diff --git a/Subsurface-mobile.pro b/Subsurface-mobile.pro
index 88e1d3ae2..161688f29 100644
--- a/Subsurface-mobile.pro
+++ b/Subsurface-mobile.pro
@@ -93,7 +93,7 @@ SOURCES += subsurface-mobile-main.cpp \
 	core/selection.cpp \
 	core/sha1.c \
 	core/string-format.cpp \
-	core/strtod.c \
+	core/strtod.cpp \
 	core/tag.cpp \
 	core/taxonomy.c \
 	core/time.cpp \
diff --git a/core/CMakeLists.txt b/core/CMakeLists.txt
index b4cc55723..0460a7bd0 100644
--- a/core/CMakeLists.txt
+++ b/core/CMakeLists.txt
@@ -169,7 +169,7 @@ set(SUBSURFACE_CORE_LIB_SRCS
 	statistics.h
 	string-format.h
 	string-format.cpp
-	strtod.c
+	strtod.cpp
 	subsurface-float.h
 	subsurface-string.cpp
 	subsurface-string.h
diff --git a/core/strtod.c b/core/strtod.cpp
similarity index 93%
rename from core/strtod.c
rename to core/strtod.cpp
index 39abfb7a7..e76ee47c0 100644
--- a/core/strtod.c
+++ b/core/strtod.cpp
@@ -109,12 +109,12 @@ no_conversion:
 	return 0.0;
 }
 
-double permissive_strtod(const char *str, const char **ptr)
+extern "C" double permissive_strtod(const char *str, const char **ptr)
 {
 	return strtod_flags(str, ptr, false);
 }
 
-double ascii_strtod(const char *str, const char **ptr)
+extern "C" double ascii_strtod(const char *str, const char **ptr)
 {
 	return strtod_flags(str, ptr, true);
 }